1. Field of the Invention
The invention concerns a steplessly variable pulling means transmission in which the variation in the transmission ratio is effected by varying the operative diameter of at least one of the pulling means pulleys over which the pulling means runs.
2. Description of the Related Art
The pulling means used can be a belt. For example a V-belt or a round belt. As well as a chain or another link-type belt or band member.
The pulling means pulleys are adapted to the respective pulling means used. In which respect. Particularly when employing round belts and V-belts. Pulleys are used whose substantially axially oriented pulling means running surfaces are slightly inclined with respect to the plane in which the endless pulling means circulates. Those pulling means pulleys whose operative diameter is variable for the purposes of varying the transmission ratio are referred to as adjusting pulleys.
In that respect it is known in the case of the described conical pulling means running surfaces for the adjusting pulley to be composed of two pulley halves which are arranged on respective sides of the plane of the pulling means and the axial spacing of which is variable whereby the operative diameter of that adjusting pulley can also be altered, by virtue of the conical configuration of the running surfaces.
It is likewise also possible for the operative diameter to be varied without axial movement, just by radial movements of the adjusting pulley, for example by virtue of the adjusting pulley being formed by segments which are possibly in mutually overlapping relationship and which are pivotable in the plane of the pulling means or which are displaceable radially relative to the axis of the adjusting pulley.
The simplest form of a pulling means transmission comprises two pulleys, over which the endless pulling means is guided, at least one of the pulleys being in the form of an adjusting pulley.
To increase the transmission ratio range, the pulling means transmission may comprise a plurality of, for example, two, pulling means which are then passed over a total of at least four pulleys. In such a situation, one belt pulley of the one pulling means is frequently carried on the same axis as a pulling means pulley of the other pulling means and is non-rotatably connected thereto, being for example of an integral construction in the form of a double pulley, as can be seen for example from DE 38 25 091.
However, it is precisely those adjusting pulleys which are varied in terms of their operative diameter by axial displacement of the pulley halves of the adjusting pulley that suffer from the problem that the plane of the pulling means is axially displaced when one pulley half is fixed and one pulley half is axially displaceable. If in that case the other pulley results in the pulling means extending in an inclined position, with the consequence of defective traction and in particular increasing wear on the pulling means.
Therefore, the attempt has already been made in DE 38 25 091 to eliminate that axial displacement by simultaneous axial movement of the carrier on which the adjusting pulleys are disposed. That however entails additional structural expenditure and also means that the adjusting pulleys are mounted in a movable member, that is to say in this case in the variator or variable speed unit, although for other reasons, for example to minimize structural size, it would be desirable if possible for the pulleys of the variator unit to be in the form of fixed pulleys which are not variable in respect of their diameter.